A steel slag-activated column for co-removal of sulfate and metals from acid mine drainage

Acid mine drainage (AMD), containing excessive sulfates and heavy metals, poses a severe threat to the environment and human health. In this study, a laboratory-scale column device using varying ratios of coarse sand to carbon steel slag (CS/CSS) as the filled material was designed to efficiently remove typical pollutants in AMD. Results revealed that the removal rates of SO₄^2-, Fe, Mn, and Zn, as well as the pH value of the solution were influenced by the ratio of CS/CSS. The highest removal rates of SO₄^2-, Fe, Mn, and Zn were 92%, 99.99%, 99.98%, and 99.99%, respectively, for CS/20%CSS. Additionally, XPS and SEM results indicated that sulfate (SO₄^2-) existed in that groups associated with CaSO₄ and Fe-sulfate complexes, while Fe, Mn, and Zn were simultaneously attached to the surface of the materials in the form of ion exchange, hydroxides, and co-precipitates. A modified sequential extraction method (BCR) results indicated that the distribution patterns of Fe, Mn, and Zn varied with increasing CSS content. Notably, when the CSS content in the column reached 20%, the metal ions were predominantly adsorbed in the top layer. The Risk Assessment Code values for Fe exhibited a low risk to the environment. These results highlight the importance of optimizing the CSS content in the permeable reactive barrier (PRB) to balance removal efficiency and permeability. Consequently, it is recommended that the content of CSS in the PRB should be maintained below 10% to ensure optimal performance and permeability. This study provides a foundation for optimizing PRB filled material design to enhance its efficiency and environmental sustainability in AMD treatment.